EP1330028B1 - Tiefpassfilter - Google Patents

Tiefpassfilter Download PDF

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Publication number
EP1330028B1
EP1330028B1 EP03000722A EP03000722A EP1330028B1 EP 1330028 B1 EP1330028 B1 EP 1330028B1 EP 03000722 A EP03000722 A EP 03000722A EP 03000722 A EP03000722 A EP 03000722A EP 1330028 B1 EP1330028 B1 EP 1330028B1
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EP
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Prior art keywords
signal
circuit
output
lpf
low
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English (en)
French (fr)
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EP1330028A3 (de
EP1330028A2 (de
Inventor
Mamoru c/o Onkyo Corporation Sekiya
Youichi c/o Onkyo Corporation Kudoh
Satomi c/o Onkyo Corporation Yamaguchi
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Onkyo Corp
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Onkyo Corp
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C27/00—Electric analogue stores, e.g. for storing instantaneous values
    • G11C27/02—Sample-and-hold arrangements
    • G11C27/024—Sample-and-hold arrangements using a capacitive memory element
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H11/00—Networks using active elements
    • H03H11/02—Multiple-port networks
    • H03H11/04—Frequency selective two-port networks

Definitions

  • the present invention generally relates to low-pass filters, and more particularly, to a low-pass filter for use in an audio apparatus.
  • EP 0 755 115 A1 discloses an active low-pass filter to be used for example in an FM demodulation circuit.
  • the filter comprises a transconductance amplifier for inputting a frequency signal and amplifying a differential voltage between a feedback voltage at an output terminal of the filter and an input voltage and output it as a current.
  • a first emitter follower is connected via a resistor to an output end of the transconductance amplifier.
  • a second emitter follower is connected via another resistor to an output end of the first-mentioned emitter follower.
  • Capacitors are provided at the output end of the transconductance amplifier and the input end of the second emitter follower, respectively.
  • a capacitor disposed between the output end of the second emitter follower and the input end of the first emitter follower is provided.
  • two resistors are provided for dividing the output voltage of the filter to feed it back to the transconductance amplifier.
  • DAC digital analog converter
  • LPF low-pass filter
  • Fig. 17 is a circuit diagram of the configuration of an LPF in a conventional audio apparatus.
  • the LPF 200 includes resistance elements R201 and R202, capacitors C201 and C202, and an operational amplifier OP201.
  • the resistance elements R201 and R202 are connected in series, and one end of the resistance element R202 is connected to the non-inverting input terminal of the operational amplifier OP201.
  • An analog signal is input to the end of the resistance element R201 not connected to the resistance element R202.
  • the capacitor C201 has its one end connected between the resistance elements R201 and R202 and its other end connected to the output terminal of the operational amplifier OP201.
  • the capacitor C202 has its one end connected to the non-inverting input terminal of the operational amplifier OP201 and its other end connected to a ground potential node 201.
  • the inverting input terminal of the operational amplifier OP201 is connected to the output terminal.
  • the LPF In order to improve the sound quality of the analog signal output from the audio apparatus, the LPF must sufficiently remove the high frequency component from the analog signal. This is because the high frequency component can be a cause of degradation of the sound quality.
  • Fig. 18 is a waveform chart of the analog signal output from the LPF 200. As shown in Fig. 18 , the LPF 200 cannot completely remove the high frequency component from the analog signal.
  • Japanese Patent No. 3,134,403 discloses the invention directed to improvement in the sound quality. According to the invention disclosed by the patent document, the waveform of the output signal is smoothed in order to improve the sound quality.
  • the high frequency component cannot fully be removed. Therefore, the high frequency component that can be a cause of degradation of the sound quality must be more thoroughly removed.
  • the object is achieved by a low-pass filter according to claim 1.
  • the voltage-current conversion circuit and the capacitance element form a filter circuit, so that the high frequency component can be significantly attenuated.
  • the differential operation circuit produces the difference between the input signal and the output signal and adds the difference to the output signal as required. Therefore, a necessary frequency component is not removed. As a result, a high sound quality can be secured.
  • the low-pass filter according to the invention includes the filter circuit after the differential operation circuit and can therefore have improved capability of removing the high frequency component.
  • the necessary frequency band is not attenuated, because the quality factor can be raised and the attenuation in the passband gain in the frequency characteristic can be restrained.
  • the low-pass filter according to the invention preferably further includes second filter circuit.
  • the second filter circuit attenuates a high frequency component of an input signal and outputs a low frequency component of the signal.
  • the differential operation circuit subtracts the output signal from the low frequency component of the input signal output from the second filter circuit and outputs a differential signal.
  • the low-pass filter can have improved capability of removing the high frequency component, because the filter order can be increased and the slope characteristic can be steeper.
  • a low-pass filter attenuates a high frequency component of an input signal and outputs a low frequency component of the signal as an output signal.
  • the low-pass filter includes differential operation circuit, sample and hold circuit, voltage-current conversion circuit, and capacitance element.
  • the differential operation circuit subtracts the output signal from the input signal and outputs a differential signal.
  • the sample and hold circuit samples and holds the differential signal output from the differential operation circuit.
  • the voltage-current conversion circuit converts voltage output from the sample and hold circuit into current.
  • the capacitance element accumulates charges in current received from the voltage-current conversion circuit and generates the output signal.
  • the low-pass filter according to the invention can sufficiently remove the high frequency component to be a cause of noise by the use of the sample and hold circuit. As a result, the high frequency component can sufficiently be removed, and the slope characteristic can be steep.
  • the sample and hold circuit preferably includes a plurality of sample and hold units and a switch circuit.
  • the plurality of sample and hold units sample and hold the differential signal in different timings from each other.
  • the switch circuit sequentially switches the outputs of the plurality of sample and hold units.
  • the plurality of sample and hold units can carry out sampling, which improves the sampling accuracy. Since errors in sampling can be reduced and the sampling period can be shortened, the output waveform can be smooth.
  • a low-pass filter includes first and second low-pass filter circuit.
  • the first low-pass filter circuit attenuates a high frequency component of an input signal and outputs a low frequency component of the signal.
  • the second low-pass filter circuit attenuates a high frequency component of the output signal of the first low-pass filter circuit and outputs a low frequency component of the signal.
  • the first low-pass filter circuit includes first differential operation circuit, sample and hold circuit, first voltage-current conversion circuit, and first capacitance element.
  • the first differential operation circuit subtracts the output signal of the first low-pass filter circuit from the input signal and outputs a differential signal.
  • the sample and hold circuit samples and holds the differential signal output from the first differential operation circuit.
  • the first voltage-current conversion circuit converts voltage output from the sample and hold circuit into current.
  • the first capacitance element accumulates charges in current received from the first voltage-current conversion circuit and generates the output signal of the first low-pass filter circuit.
  • the second low-pass filter circuit includes second differential operation circuit, second voltage-current conversion circuit, and second capacitance element.
  • the second differential operation circuit subtracts the output signal of the second low-pass filter circuit from the output signal of the first low-pass filter circuit and outputs a differential signal.
  • the second voltage-current conversion circuit converts voltage output from the second differential operation circuit into current.
  • the second capacitance element accumulates charges in current received from the second voltage-current conversion circuit and generates the output signal of the second low-pass filter circuit.
  • the low-pass filter according to the invention includes the two low-pass filter circuit.
  • the output signal of the first low-pass filter circuit is further removed of the high frequency component by the second low-pass filter circuit.
  • the output signal of the first low-pass filter circuit can have a smoother waveform by the use of the second low-pass filter circuit.
  • Fig. 1 is a functional block diagram of the configuration of an LPF according to an embodiment of the invention.
  • the LPF 700 includes a differential operation circuit 2, a voltage-current conversion circuit 3, and a capacitor C1.
  • a DAC 7 converts an externally input digital signal into an analog signal ⁇ A.
  • the differential operation circuit 2 obtains the differential value between the analog signal ⁇ A output from the DAC 7 and an output signal ⁇ B fed back from an output node N1. More specifically, the differential operation circuit 2 subtracts the output signal ⁇ B from the analog signal ⁇ A to output a differential signal ⁇ C.
  • the voltage-current conversion circuit 3 receives the output signal of the differential operation circuit 2 and converts the voltage value into a current value.
  • Fig. 2 is a circuit diagram of a typical voltage-current conversion circuit.
  • the voltage-current conversion circuit 3 includes resistance elements R31 to R36 and an operational amplifier OP31.
  • the resistance element R31 has its one end connected to the inverting input terminal of the operational amplifier OP31, and its other end receives an output signal from the differential operation circuit 2.
  • the resistance element R32 has its one end connected to the inverting input terminal of the operational amplifier OP31 and its other end connected to the resistance element R33.
  • the resistance element R33 has its other end connected to the output terminal of the operational amplifier OP31.
  • the resistance element R34 has its one end connected to the output terminal of the operational amplifier OP31 and its other end connected to the resistance element R35.
  • the other end of the resistance element R35 is connected to the non-inverting input terminal of the operation amplifier OP31.
  • the resistance element R36 has its one end connected to the non-inverting input terminal of the operational amplifier OP31 and its other end connected to a ground potential node 201.
  • the voltage-current conversion circuit 3 shown in Fig. 2 is a constant current circuit in which output resistance is equivalently raised by positive feedback.
  • the capacitor C1 has its one end connected to the voltage-current conversion circuit 3 at the node N1 and its other end connected to the ground potential node 201.
  • the capacitor C1 is charged or discharged by current output from the voltage-current conversion circuit 3.
  • the voltage-current conversion circuit 3 and the capacitor C1 form a filter circuit 4.
  • the filter circuit 4 outputs the output signal ⁇ B from the output node N1.
  • Fig. 3 is a waveform chart for use in illustration of the operation of the LPF 700.
  • the axis of ordinate represents voltage V
  • the axis of abscissa represents time t.
  • the analog signal ⁇ A contains a high frequency component to be a cause of noise. Meanwhile, the output signal ⁇ B is removed of a high frequency component by the filter circuit 4.
  • the differential signal ⁇ C equals to the difference between the analog signal ⁇ A and the output signal ⁇ B and therefore contains the high frequency component to be a cause of noise.
  • ⁇ C ⁇ A - ⁇ B
  • the differential operation circuit 2 outputs the differential signal ⁇ C whose voltage value is zero.
  • the differential signal ⁇ C is a negative function whose value is minimized at time t1'. Therefore, from time t1 to t2, the capacitor C1 is discharged. This causes the output signal ⁇ B to drop.
  • the differential signal ⁇ C is a positive function whose value is maximized at time t2'. Therefore, from time t2 to t3, the capacitor C1 is charged. This causes the output signal ⁇ B to rise.
  • the transition of the differential signal ⁇ C and the output signal ⁇ B after time t3 is the same as that from time t1 to t3, and therefore will not be described.
  • the differential operation circuit 2 allows the output signal ⁇ B output from the LPF 700 to have substantially the same phase and level (amplitude) as those of the analog signal ⁇ A. If the LPF 700 is not provided with the differential operation circuit 2, the capacitor C1 is saturated at the power supply voltage for the operational amplifier OP31. As a result, the LPF no longer performs normal circuit operation. In the LPF without the differential operation circuit 2, an output signal in a phase and a level different from the analog signal is output.
  • the LPF 700 allows the differential operation circuit 2 to calculate the differential value between the analog signal and the output signal, and therefore the necessary frequency band is not attenuated.
  • the LPF 700 further includes a filter circuit 4 between the differential operation circuit 2 and the output node N1.
  • the voltage-current conversion circuit 3 has high resistance, so that the filter circuit 4 has a large time constant. Therefore, the high frequency component can sufficiently be removed from the output signal ⁇ B.
  • Fig. 4 is a block diagram of the configuration of an LPF according to another embodiment of the invention.
  • the LPF 400 includes a sample and hold circuit 8 and a control circuit 20 in addition to the configuration of the LPF 700.
  • the control circuit 20 outputs a sampling signal ⁇ S to control the sample and hold circuit 8.
  • the other part of the circuit configuration is the same as that of the LPF 700 and therefore will not be described.
  • Fig. 5 is a circuit diagram showing in detail the configuration of the sample and hold circuit 8 in Fig. 4 .
  • the sample and hold circuit 8 includes a first hold circuit 9, a second hold circuit 10 and a switch circuit 11.
  • the first and second hold circuits 9 and 10 are connected in parallel and have their input terminals both provided with the differential signal ⁇ C as an input.
  • the first and second hold circuits 9 and 10 have their output terminals both connected to the switch circuit 11.
  • the first hold circuit 9 includes a switching element SW1 and a capacitor C2.
  • the switching element SW1 is provided with the differential signal ⁇ C at its one end, and its other end is connected to the switch circuit 11.
  • the capacitor C2 has its one end connected between the switching element SW1 and the switch circuit 11 and its other end connected to the ground potential node 201.
  • the sampling signal ⁇ S is in an H level
  • the switching element SW1 in the first hold circuit 9 is turned on, and charges are accumulated in the capacitor C2.
  • the sampling signal ⁇ S is in an L level
  • the switching element SW1 is turned off.
  • the signal output from the first hold circuit 9 is designated as signal ⁇ D1.
  • the second hold circuit 10 includes a switching element SW2 and a capacitor C3.
  • the switching element SW2 is provided with the differential signal ⁇ C at its one end, and its other end is connected to the switch circuit 11.
  • the capacitor C3 has its one end connected between the switching element SW2 and the switch circuit 11 and its other end is connected to the ground potential node 201.
  • the sampling signal ⁇ S is in an L level
  • the switching element SW2 in the second hold circuit 10 is turned on, and charges are accumulated in the capacitor C3.
  • the sampling signal ⁇ S is in an H level
  • the switching element SW2 is turned off.
  • the signal output from the second hold circuit 10 is designated as signal ⁇ D2.
  • the switch circuit 11 includes a switching element SW3.
  • the switching element SW3 includes input nodes Na and Nb and an output node N2.
  • the sampling signal ⁇ S is in an L level
  • the input node Na and the output node N2 in the switching element SW3 are connected.
  • the sampling signal ⁇ S is in an H level
  • the input node Nb and the output node N2 are connected.
  • the signal output from the switching element SW3 is designated as signal ⁇ D.
  • Fig. 6 is a waveform chart for use in illustration of the operation of the LPF 400 shown in Fig. 4 .
  • the three waveforms shown in Fig. 6 represent the differential signal ⁇ C, the signal ⁇ D output from the sample and hold circuit 8, and the output signal ⁇ B.
  • the differential signal ⁇ C equals the difference between the analog signal ⁇ A output from the DAC 7 and the output signal ⁇ B.
  • the analog signal ⁇ A contains a high frequency component to be a cause of noise, and therefore the differential signal ⁇ C also contains a high frequency component.
  • the sample and hold circuit 8 samples the differential signal ⁇ C at prescribed intervals in response to the sampling signal ⁇ S output from the control circuit 20 and holds the sampled voltage. As a result, the sample and hold circuit 8 outputs the signal ⁇ D in a stepped form as shown in Fig. 6 .
  • Fig. 7 is a waveform chart for use in illustration of the operation of the sample and hold circuit 8 in Fig. 4 .
  • the first and second hold circuits 9 and 10 are both provided with the differential signal ⁇ C.
  • the sampling signal ⁇ S output from the control circuit 20 attains an H level.
  • the switching element SW1 in the first hold circuit 9 is turned on.
  • the capacitor C2 is therefore charged.
  • the signal ⁇ D1 output from the first hold circuit 9 has a waveform equivalent to the signal ⁇ C.
  • the switching element SW2 is turned off.
  • the signal ⁇ D2 output from the second hold circuit 10 attains a voltage level based on charges accumulated in the capacitor C3 before period T1.
  • the high frequency component contained in the differential signal ⁇ C is removed.
  • the switch circuit 11 has its input node Nb and its output node N2 connected because the sampling signal ⁇ S is in the H level. Therefore, the switch circuit 11 outputs the signal ⁇ D2 output from the second hold circuit 10 as the output signal ⁇ D.
  • the sampling signal ⁇ S attains an L level.
  • the switching element SW1 in the first hold circuit 9 is turned off.
  • the signal ⁇ D1 therefore attains a level of voltage charged in the capacitor C2 up to the moment immediately before period T2.
  • the high frequency component contained in the differential signal ⁇ C is removed.
  • the switching element SW2 in the second hold circuit 10 is turned on, and the capacitor C3 is charged by the differential signal ⁇ C.
  • the input node Na and the output node N2 are connected in the switch circuit 11. Then, the signal ⁇ D1 is output as the output signal ⁇ D.
  • the switch circuit 11 outputs the hold voltage removed of the high frequency component as the output signal ⁇ D in periods T1 and T2.
  • the signal ⁇ D output from the sample and hold circuit 8 therefore has a stepped waveform as shown in Fig. 6 or 7 .
  • the sample and hold circuit 8 can control which high frequency component to remove from the differential signal ⁇ C depending on the frequency of the sampling signal ⁇ S output from the control circuit 20. More specifically, when for example the sampling signal ⁇ S is at 700 KHz, a signal at a higher frequency than 700 KHz is removed as the high frequency component.
  • the output signal ⁇ D output from the sample and hold circuit 8 is input to the filter circuit 4.
  • the stepped waveform is then shaped into the smooth waveform of the output signal ⁇ B in the filter circuit 4.
  • the output signal ⁇ B output from the filter circuit 4 has a smooth waveform as shown in Fig. 8 .
  • Fig. 9 is a graph showing the frequency characteristic of the LPF 400 shown in Fig. 4 .
  • the sampling frequency in this case is 700 KHz.
  • the slope characteristic becomes steep around above 700 KHz.
  • the LPF 400 shown in Fig. 4 can sufficiently remove a high frequency component that can be a cause of noise.
  • the LPF 400 includes the two hold circuits 9 and 10 in the sample and hold circuit 8. In this way, while one hold circuit outputs voltage held by it, the other hold circuit can sample a signal. Therefore, when the sampling period for the voltage of the differential signal ⁇ C is shortened, the voltage value can accurately be sampled. Note that there are these two hold circuits in Fig. 5 , while more than two hold circuits may be provided to shorten the sampling period and carry out more accurate sampling. In this case, the number of input nodes of the switch circuit 11 is equal to the number of hold circuits to be provided.
  • Fig. 10 is a circuit diagram of the configuration of an LPF according to another embodiment of the invention.
  • the LPF 600 includes a filter circuit 12 in addition to the configuration of the LPF 700.
  • the filter circuit 12 is connected between the DAC 7 and the differential operation circuit 2.
  • the other part of the configuration is the same as that shown in Fig. 1 and therefore will not be described.
  • the LPF 600 includes the filter circuits 12 and 4.
  • the LPF 600 is therefore a secondary filter circuit.
  • the LPF can have steeper slope characteristics for higher orders. Therefore, the LPF 600 can more thoroughly remove the high frequency component that can be a cause of noise.
  • Fig. 11 is a circuit diagram of the configuration of an LPF according to another embodiment of the invention.
  • the LPF 100 includes a differential operation circuit 2, a voltage-current conversion circuit 3, a filter circuit 15, and a capacitor C1.
  • the filter circuit 15 is connected between the differential operation circuit 2 and the voltage-current conversion circuit 3.
  • the other part of the circuit configuration is the same as that shown in Fig. 1 and therefore will not be described.
  • the LPF 600 has the filter circuit 12 inserted before the differential operation circuit 2 as shown in Fig. 10 .
  • Fig. 12 is a graph showing the frequency characteristics of the LPF 100 and the LPF 600.
  • the frequency characteristic of the LPF 100 is denoted by FA and the frequency characteristic of LPF 600 is denoted by FB.
  • the slope characteristics of the frequency characteristics FA and FB are substantially equal. This is because the LPF 100 and the LPF 600 both form a secondary filter.
  • the attenuation in the passband gain in the frequency characteristic FA is smaller than that in the frequency characteristic FB. This is for the following reason.
  • a quality factor (hereinafter referred to as "Q value") defines the frequency characteristic of an LPF.
  • Q value When the Q value is raised, electrical signals in the passband in the frequency characteristic are amplified. Therefore, when the Q value can be raised as desired, the attenuation in the passband gain in the frequency characteristic can be restrained.
  • R 1 is the resistance value of the resistance element R1, C 1 the capacitance of the capacitor C1, C 4 the capacitance of the capacitor C4, and G the voltage-current conversion constant of the voltage-current conversion circuit 3.
  • the Q value of the LPF 100 can be raised depending on the combination of the resistance R 1 , the capacitance C 1 , C 4 and the voltage-current conversion constant G.
  • the Q value Q 600 of the LPF 600 is given by the following expression:
  • the Q value of the LPF 600 is not larger than 1/ 2 by any combination of R 1 , C 1 , C 4 , and G.
  • the Q value of the LPF 100 having the filter circuit 15 inserted after the differential operation circuit 2 can be higher than that of the LPF 600 having the filter circuit 12 inserted before the differential operation circuit 2. Therefore, the attenuation in the passband gain in the frequency characteristic FA can be more restrained than that in the frequency characteristic FB.
  • the LPF 700 has a configuration equivalent to the configuration the LPF 100 as shown in Fig. 1 excluding the filter circuit 15.
  • Fig. 13 is a graph showing the frequency characteristics of the LPFs 100 and 700.
  • the LPF 700 is a primary filter, while the LPF 100 is a secondary filter and therefore the frequency characteristic FA of the LPF 100 has a steeper slope characteristic than the frequency characteristic FC of the LPF 700.
  • the attenuation in the passband gain is more restrained than in the frequency characteristic FC. This is because the primary filter, LPF 700 cannot control the passband gain in the frequency characteristic, but the secondary filter, LPF 100 can raise the Q value and restrain the passband gain in the frequency characteristic.
  • the LPF 100 having the filter circuit 15 after the differential operation circuit 2 can restrain the attenuation in the passband gain in the frequency characteristic. Consequently, the LPF 100 can remove the high frequency component to be a cause of noise.
  • Fig. 14 is a circuit diagram of the configuration of an LPF according to another embodiment of the invention.
  • the LPF 200 includes a filter circuit 13 between the DAC 7 and the differential operation circuit 2 in addition to the configuration of the LPF 100.
  • the filter circuit 13 includes a resistance element R2 and a capacitor C5.
  • the resistance element R2 is connected between the DAC 7 and the differential amplifier circuit 2.
  • the capacitor C5 has its one end connected between the resistance element R2 and the differential operation circuit 2 and its other end connected to the ground potential node 201.
  • the other part of the configuration is the same as that of the LPF 100 and will not be described.
  • the LPF 200 is a tertiary filter, in other words, a higher order filter than the LPF 100.
  • the frequency characteristic of the LPF 200 has a steeper slope than that of the frequency characteristic of the LPF 100, and a higher frequency component can be removed.
  • Fig. 15 is a circuit diagram of the configuration of an LPF according to another embodiment of the invention.
  • the LPF 900 includes a filter circuit 14 between the DAC 7 and the output node N1 in addition to the configuration of the LPF 200.
  • the other part of the circuit configuration is the same as that of the LPF 200.
  • the filter circuit 14 includes a resistance element R3 and a capacitor C1. Note that the filter circuit 14 and the filter circuit 4 share the capacitor C1.
  • the differential signal ⁇ C output from the differential operation circuit 2 is converted into a current value by the voltage-current conversion circuit 3, and the capacitor C1 is charged (or discharged). Since the filter circuit 14 and the filter circuit 4 share the capacitor C1, the output signal ⁇ B is produced as the sum of the output signal of the filter circuit 14 and the output signal of the filter circuit 4. Then, the sum is fed back to the differential operation circuit 2.
  • the time constant of the filter circuit 14 is larger than that of the filter circuit 13.
  • the filter circuit 14 therefore has greater capability of removing the high frequency component.
  • the output signal of the filter circuit 14 is added to the output signal of the filter circuit 4 and the sum is output as the output signal ⁇ B from the LPF 900. This allows the high frequency component to be removed from the output signal ⁇ B.
  • the differential operation circuit 2 produces the difference between the output signal of the filter circuit 13 and the output signal ⁇ B and the capacitor C1 is charged (or discharged) based on the differential value, so that the necessary frequency band can be prevented from being attenuated.
  • the LPF 900 has a higher filter order and may have a steeper slope characteristic.
  • Fig. 16 is a diagram of the configuration of an LPF according to another embodiment of the invention.
  • the LPF 500 includes a differential operation circuit 22, a voltage-current conversion circuit 23 and a capacitor C5 in addition to the configuration of the LPF 400 shown in Fig. 4 .
  • the differential operation circuit 22 is connected between the node N1 and the voltage-current conversion circuit 23.
  • the capacitor C5 has its one end connected to the output terminal of the voltage-current conversion circuit 23 and its other end connected to the ground potential node 201.
  • the voltage-current conversion circuit 23 and the capacitor C5 form a filter circuit 40.
  • the LPF 500 outputs an output signal ⁇ E from the output node N21.
  • Node N21 is the connection node of the voltage-current conversion circuit 23 and the capacitor C5.
  • the differential operation circuit 22 outputs the differential value between the output signals ⁇ B and ⁇ E from the node N1.
  • the other part of the configuration is the same as that of the LPF 400 and will not be described.
  • the LPF 500 as described above generates an output signal ⁇ B removed of a high frequency component by the sample and hold circuit 8.
  • the vector shaped output signal ⁇ B is shaped into a very smooth output signal ⁇ E.
  • the LPF can remove the high frequency component with the sample and hold circuit, but when the sampling frequency of the sampling signal ⁇ S is low, the waveform of the output signal ⁇ B might not be smooth.
  • the LPF 500 can remove the high frequency component and then shape the waveform of the output signal into a smooth form.

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Claims (5)

  1. Tiefpassfilter für die Verwendung in einer Audiovorrichtung und zum Abschwächen einer Hochfrequenzkomponente eines Eingangssignals (ϕA) und zum Ausgeben einer Niederfrequenzkomponente des Eingangssignals (ϕA) als ein Ausgangssignal (ϕB) mit:
    einem Differenzbildungsmittel (2) zum Subtrahieren des Ausgangssignals (ϕB) von dem Eingangssignal (ϕA) und zum Ausgeben eines Differenzsignals (ϕC);
    einem Spannungs-Strom-Umwandlungsmittel (3) zum Umwandeln der Spannung des von dem Differenzbildungsmittel (2) ausgegebenen Differenzsignals (ϕC) in einen Strom;
    einem Kapazitätsmittel (C1) zum Akkumulieren von Ladungen aus dem Strom, der von dem Spannungs-Strom-Umwandlungsmittel (3) entgegengenommen wird, zum Erzeugen des Ausgangssignals (ϕB); und
    einem ersten Filtermittel (15), das zwischen das Differenzbildungsmittel (2) und das Spannungs-Strom-Umwandlungsmittel (3) geschaltet ist zum Abschwächen einer Hochfrequenzkomponente des Differenzsignals (ϕC), das von dem Differenzbildungsmittel (2) ausgegeben wird, und zum Ausgeben einer Niederfrequenzkomponente des Differenzsignals (ϕC) zur Zuführung zu dem Spannungs-Strom-Umwandlungsmittel (3).
  2. Tiefpassfilter nach Anspruch 1, weiterhin aufweisend:
    ein zweites Filtermittel (13) zum Abschwächen einer Hochfrequenzkomponente des Eingangssignals (ϕA) und zum Ausgeben einer Niederfrequenzkomponente des Eingangssignals (ϕA),
    wobei das Differenzbildungsmittel (2) das Ausgangssignal (ϕB) von der Niederfrequenzkomponente des Eingangssignals (ϕA), das von dem zweiten Filtermittel (13) ausgegeben wird, subtrahiert zum Ausgeben des Differenzsignals (ϕC).
  3. Tiefpassfilter, das eine Hochfrequenzkomponente eines Eingangssignals (ϕA) abschwächt und eine Niederfrequenzkomponente des Eingangssignals (ϕA) ausgibt als ein Ausgangssignal (ϕB) mit:
    einem Differenzbildungsmittel (2) zum Subtrahieren des Ausgangssignals (ϕB) von dem Eingangssignal (ϕA) und zum Ausgeben eines Differenzsignals (ϕC);
    einem Abtasthaltemittel (8) zum Abtasten und Halten des Differenzsignals (ϕC), das von dem Differenzbildungsmittel (2) ausgegeben wird;
    einem Spannungs-Strom-Umwandlungsmittel (3) zum Umwandeln der Spannung, die von dem Abtasthaltemittel (8) ausgegeben wird, in einen Strom; und
    einem Kapazitätsmittel (C1) zum Akkumulieren von Ladungen in dem Strom, der von dem Spannungs-Strom-Umwandlungsmittel (3) empfangen wird, zum Erzeugen des Ausgangssignals (ϕB).
  4. Tiefpassfilter nach Anspruch 3, bei dem das Abtasthaltemittel (8) aufweist:
    eine Mehrzahl von Abtasthalteschaltungen (9, 10), welche das Differenzsignal (ϕC) zu zueinander unterschiedlichen Zeitpunkten abtasten und halten; und
    eine Umschaltschaltung (11), die sequentiell die Ausgänge der Mehrzahl von Abtasthalteschaltungen (9, 10) schaltet.
  5. Tiefpassfilter mit:
    einem ersten Tiefpassfiltermittel nach Anspruch 3 und
    einem zweiten Tiefpassfiltermittel zum Abschwächen einer Hochfrequenzkomponente des Ausgangssignals (ϕB) von dem ersten Tiefpassfiltermittel und zum Ausgeben einer Niederfrequenzkomponente des Ausgangssignals (ϕB),
    wobei das zweite Tiefpassfiltermittel aufweist:
    ein zweites Differenzbildungsmittel (22) zum Subtrahieren des Ausgangssignals (ϕE) des zweiten Tiefpassfiltermittels von dem Ausgangssignal (ϕB) des ersten Tiefpassfiltermittels und zum Ausgeben eines Differenzsignals;
    einem zweiten Spannungs-Strom-Umwandlungsmittel (23) zum Umwandeln der Spannung, die von dem zweiten Differenzbildungsmittel (22) ausgegeben wird, in einen Strom; und
    ein zweites Kapazitätsmittel (C5) zum Akkumulieren von Ladungen in dem Strom, der von dem zweiten Spannungs-Strom-Umwandlungsmittel (23) empfangen wird, zum Erzeugen des Ausgangssignals (ϕE) des zweiten Tiefpassfiltermittels.
EP03000722A 2002-01-17 2003-01-13 Tiefpassfilter Expired - Lifetime EP1330028B1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP2002009176 2002-01-17
JP2002009176 2002-01-17
JP2002340528A JP3616878B2 (ja) 2002-01-17 2002-11-25 低域通過フィルタ
JP2002340528 2002-11-25

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EP1330028A2 EP1330028A2 (de) 2003-07-23
EP1330028A3 EP1330028A3 (de) 2005-08-10
EP1330028B1 true EP1330028B1 (de) 2008-11-19

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EP03000722A Expired - Lifetime EP1330028B1 (de) 2002-01-17 2003-01-13 Tiefpassfilter

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DE (1) DE60324719D1 (de)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3978744B2 (ja) * 2002-07-25 2007-09-19 パイオニア株式会社 デジタルアナログ変換器
TWI312238B (en) * 2006-04-24 2009-07-11 Ind Tech Res Inst Delay line and analog-to-digital converting apparatus and load-sensing circuit using the same
JP4026665B1 (ja) * 2006-09-07 2007-12-26 オンキヨー株式会社 ローパスフィルタ及びそれに用いられる電圧電流変換回路
US7626527B1 (en) * 2008-07-09 2009-12-01 Newport Media, Inc. Continuous time sigma-delta analog-to-digital converter with stability
CN103840646B (zh) * 2012-11-23 2017-03-01 南京博兰得电子科技有限公司 一种谐振变换装置

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5545112A (en) * 1978-09-22 1980-03-29 Sony Corp Signal transmitter
JP3134403B2 (ja) 1991-09-09 2001-02-13 オンキヨー株式会社 デジタル／アナログ変換器
JP3125225B2 (ja) 1992-03-25 2001-01-15 オンキヨー株式会社 デジタル／アナログ変換器
DE19524409C1 (de) * 1995-07-04 1996-08-08 Siemens Ag Filterschaltung mit veränderbarer Übertragungsfunktion
JPH0936702A (ja) * 1995-07-20 1997-02-07 Nippon Motorola Ltd アクティブロ−パスフィルタ
KR100298090B1 (ko) * 1996-03-01 2001-10-27 모리시타 요이찌 주파수의존저항기

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DE60324719D1 (de) 2009-01-02
JP2003283299A (ja) 2003-10-03
US6697002B2 (en) 2004-02-24
US20030132869A1 (en) 2003-07-17
EP1330028A3 (de) 2005-08-10
JP3616878B2 (ja) 2005-02-02
EP1330028A2 (de) 2003-07-23

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